Circulating IL-6, IL-10, and TNF-alpha and IL-10/IL-6 and IL-10/TNF-alpha ratio profiles of polyparasitized individuals in rural and urban areas of gabon

Abstract

Malaria, blood-borne filarial worms and intestinal parasites are all endemic in Gabon. This geographical co-distribution leads to polyparasitism and, consequently, the possibility of immune-mediated interactions among different parasite species. Intestinal protozoa and helminths could modulate antimalarial immunity, for example, thereby potentially increasing or reducing susceptibility to malaria. The aim of the study was to compare the cytokine levels and cytokine ratios according to parasitic profiles of the population to determine the potential role of co-endemic parasites in the malaria susceptibility of populations. Blood and stool samples were collected during cross-sectional surveys in five provinces of Gabon. Parasitological diagnosis was performed to detect plasmodial parasites, Loa loa, Mansonella perstans, intestinal helminths (STHs) and protozoan parasites. Nested PCR was used to detect submicroscopic plasmodial infection in individuals with negative blood smears. A cytometric bead array was used to quantify interleukin (IL)-6, IL-10 and tumour necrosis factor (TNF)-α in the plasma of subjects with different parasitological profiles. Median IL-6 and IL-10 levels and the median IL-10/TNF-α ratio were all significantly higher among individuals with Plasmodium (P.) falciparum infection than among other participants (p<0.0001). The median TNF-α level and IL-10/IL-6 ratio were higher in subjects with STHs (p = 0.09) and P. falciparum-intestinal protozoa co-infection (p = 0.04), respectively. IL-6 (r = -0.37; P<0.01) and IL-10 (r = -0.37; P<0.01) levels and the IL-10/TNF-α ratio (r = -0.36; P<0.01) correlated negatively with age. Among children under five years old, the IL-10/TNF-α and IL-10/IL-6 ratios were higher in those with intestinal protozoan infections than in uninfected children. The IL-10/TNF-α ratio was also higher in children aged 5-15 years and in adults harbouring blood-borne filariae than in their control counterparts, whereas the IL-10/IL-6 ratio was lower in those aged 5-15 years with filariae and intestinal parasites but higher in adults with intestinal parasitic infections. Asymptomatic malaria is associated with a strong polarization towards a regulatory immune response, presenting high circulating levels of IL-10. P. falciparum/intestinal protozoa co-infections were associated with an enhanced IL-10 response. Immunity against malaria could differ according to age and carriage of other parasites. Helminths and intestinal protozoa can play a role in the high susceptibility to malaria currently observed in some areas of Gabon, but further investigations are necessary.

Fig 1. Flow chart of the study population.

This figure represents a flow chart for enrolment of the study population, followed by the number of individuals found with malarial infections in the study population and absolute frequencies in each group with different parasitic profiles.

Fig 2. Comparisons of cytokine concentrations between groups with different parasitic profiles.

The p value considered significant for analysis presented in this graphic is 0.000357. Only p values with two or more zero after the full stop of the decimal part were presented in the figure. All the associations showed no significant difference. (A) Box plot displaying IL-6, TNF-α and IL-10 cytokine production and IL-10/TNF-α and IL-10/IL-6 median ratios according to different parasitic profiles. The Mann–Whitney test was carried out for pairwise comparisons. Values used for the graphical representation were log-transformed. (B): Comparisons in rural areas only because there were not enough data for urban areas to perform this analysis.

Fig 3. Cytokines profiles stratified by areas according to age in months. IL-10 level decreased when age increased in rural area. IL-10/TNF-alpha ratio increased with age in rural area but decreased in urban area.

Fig 4. Study sites where samples were collected.

Map of Gabon with the names of the nine (9) provinces. The black dots on the map correspond to the capitals of each province. Red circles represent many villages around the site, and red full stops indicate a site. Libreville, Oyem and Koula-Moutou are represented in red full stop to indicate study sites but are also capitals of province. Blue indicates the names of sites that patients were recruited from for the present study. Map adapted from: [16].